Prior to the development of the CED device, prior art practitioners employed mechanical devices which were powered by conventional rotary electric motors. Such devices were typically inflexible, mechanically complex, bulky, heavy, noisy, costly, energy-inefficient, subject to wear, and incapable of producing precisely controlled, very rapid movement. Furthermore, attempts to overcome the disadvantages of such mechanical devices by development of electric devices resulted in inefficiency of operation, as well as in undesirable size and cost of the device. In addition, the various disadvantages pointed out above were not satisfactorily eliminated.
Electrical translatory devices, such as solenoids and reed relays, proved inflexible in that they were unable to control their movements, other than by mechanical springs or stops. Such inflexibility of the prior art devices also manifested itself in the form of an inability to accomplish sophisticated movements, such as complex planar or three-dimensional curves. Finally, the prior art devices were hampered by operational disadvantages, including overshoot, hunting and ringing. Such devices were generally used in an on-off mode.
Arrangements of the prior art have included a mechanical spring. However, the mechanical spring is burdened with the following drawbacks: the spring constant is not constant over the full range of possible tension or compression of the spring; the spring constant is not the same in tension as it is in compression; the spring constant changes with age and mechanical fatigue; the spring constant cannot be varied at will; and the spring resistance cannot be completely eliminated, making it necessary either to apply force continuously or to use a locking mechanism to maintain a desired displacement position.